The present invention relates generally to an antenna for establishing communication with multiple transmitting and receiving sources, such as satellites. More particularly, the multibeam antenna of the present invention relates to an antenna for establishing communication with satellites which are located at geostationary positions that are in close angular proximity to each other.
In recent years, there has been a significant increase in the amount and types of information that is transmitted via satellite communication. For instance, satellites now transmit telephone signals, television signals, and Internet data, etc. Due to the expanded use of satellites for data communication, there has also been an associated increase in the number of satellites placed in orbit about the earth. For instance, there are currently satellites that are dedicated to transmission of not only television signals in general, but are dedicated to transmission of only certain types of programming, such as movie channels, foreign language channels, local channel programming, or high definition television signals. Further, satellites have been deployed for Internet communication.
Due to the increasing amount of information and services that are offered via satellite communication, there exists a current need for an integrated antenna that can transmit and receive signals to and from different satellites each located at different geostationary positions, such that a user is not required to use multiple antennas. This, however, presents an increasing problem with the introduction of additional satellites into orbit for different types of data communication. As more satellites are introduced into orbit, the angular spacing between the satellites will decrease. In fact, currently there are several satellites that are positioned within a range of 5 degrees or less of arc with respect to each other. The proximity of these satellites to each other is somewhat problematic from the standpoint of using one antenna to establish individual communication links with both of these satellites.
Specifically, to communicate with multiple satellites, an antenna will typically include individual antenna elements, referred to as feeds or more generally, wave-guides, where each feed is dedicated to communicating with one of the satellites. Because of the closeness in angular proximity of some satellites, these wave-guides should be placed in close proximity to each other on the antenna to properly communicate with their respective satellites. The problem is that many conventional corrugated wave-guide designs cannot be used, because of the reduced spacing required between the phase centers of the wave-guides needed to receive from and transmit signals to the satellites is such that the conventional individual wave-guides would occupy overlapping space due to their size.
This problem is more clearly illustrated with reference to FIGS. 1A and 1B. FIG. 1A illustrates a typical satellite system 10 having two satellites, 12 and 14, located at geostationary positions that are a particular arc distance 16 apart. The satellite system further includes either one or a plurality of ground-based antennas, 18-22, for communication with these satellites. In particular, each of the ground-based antennas typically includes a reflector 22 directed toward the satellites. Each of the antennas also includes respective individual wave-guides, 24 and 26, for establishing communication links with the individual satellites. The wave-guides are positioned with respect to the reflector so that signals 28 received from the satellite associated with the wave-guides are directed by the reflector to the wave-guides and signals from the wave-guides are directed by the reflector to the associated satellite. As the wave-guides are positioned with respect to the reflector to receive signals from and transmit signals to their associated satellite, problems occur when the satellites with which the individual wave-guides respectively communicate are located in close angular proximity to each other.
Specifically, FIG. 1B shows two signals, 30 and 32, respectively transmitted by two individual satellites to an antenna 34. In this illustration, the reflector 36 of the antenna is directed at a first satellite, and the signals 30 from this satellite are reflected by the reflector to a focal point 38 in front of the reflector. Further, the signals 32 received from the second satellite are directed by the reflector to a second point 40 in front of the reflector. In this instance, the wave-guide 42 associated with the first satellite is located at the focal point 38, and the wave-guide 44 associated with the second satellite is located at the second point 40 to thereby establish respective communication links with the satellites.
As can be seen, there is an offset distance 46 between the wave-guides. This offset distance is determined by the angular difference between the geostationary positions of the satellites. If the satellites are located at geostationary positions that are farther apart angularly, then there will be a larger offset distance 46 between the wave-guides. However, the closer the satellites are positioned with respect to each other, the smaller the offset distance 46 becomes. At some point, typically when the satellites are spaced apart by an angular distance of 5xc2x0 or less, the offset distance between the wave-guides becomes sufficiently small, such that many conventional corrugated wave-guide designs cannot be used. Specifically, the spacing required between the phase centers of the wave-guides to properly receive and transmit signals to the satellites is such that the conventional individual wave-guides would occupy overlapping space due to their size.
To address this problem, an antenna system has been designed to allow for more closely spaced receive feeds, as described in U.S. Pat. No. 5,812,096 to Tilford. With reference to FIG. 2, this antenna system 50 includes a reflector 52 and a feed system in which two conventional receive feeds, 54 and 56, have been modified such that they may be spaced a reduced distance apart. This feed configuration is referred to as a siamese feed, in which a section of the housing for each conventional feed has been cutaway so that the feeds may be spaced closer together. The siamese feed allows for reception of signals, 30 and 32, from two closely spaced satellites.
Although the siamese feed of this antenna system allows for communication with closely spaced satellites, it does have some drawbacks. For example, first the siamese feed does not use standard wave-guides. Instead, the wave-guides must be modified by removing a portion of their housing. This, in turn, may increase manufacturing time and cost.
Further, the siamese feed system does not provide a solution for antennas that establish two-way communication with satellites. This is a significant limitation of the siamese feed system. Specifically, certain commercial systems employ one satellite used for Internet communication and in close proximity to this particular satellite is another satellite used for transmission of high definition television. Since the siamese feed system only includes receive wave-guides, and not a bidirectional wave-guide for two-way communication, it would not be suitable for this antenna application.
An added problem with placement of wave-guides in close proximity to each other, besides physical size limitations, not addressed by the siamese feed system is signal isolation concerns. Specifically, in applications in which the antenna is used in a two-way communication application, signals transmitted from a bi-directional wave-guide to a satellite are also broadcast to the area surrounding the wave-guide. If a second wave-guide is positioned in close proximity to communicate with another closely angular spaced satellite, the transmission signals from the first wave-guide may be received by the second wave-guide, thereby possibly disrupting communication between the closely spaced second wave-guide and its associated satellite.
As set forth below, the present invention provides antennas and multiplexer structures that overcome many of the identified deficiencies and several additional deficiencies associated with establishing communication with satellites that are positioned in close angular proximity to each other. Specifically, the antennas and multiplexer structures of the present invention include wave-guides that can be spaced in close proximity to each other so as to establish data communication with satellites that are located in close angular proximity to each other. As such, the present invention may provide an antenna having one reflector and multiple wave-guides for data communication with a plurality of satellites, including satellites that are in close proximity to one another, such that a user may establish desired communication links with the different satellites without the need for additional antennas.
In addition, the present invention also provides antennas and multiplexer structures that may be manufactured at a reduced cost. Specifically, in some embodiments of the present invention, the antenna and multiplexer structures use commercially available wave-guides that do not require substantial modification prior to use. As such, manufacturing time and cost may be reduced. Further, the antennas and multiplexer structures of the present invention use isolation structures and methods that reduce the propagation of signals transmitted by one closely spaced feedhorn section of a wave-guide from propagating along the receive wave-guide section of an adjacent wave-guide. They also prevent transmit signals transmitted on the transmit wave-guide section of a wave-guide from propagating along the receive wave-guide section of the wave-guide and signals received by the feedhorn section of the wave-guide from propagating along the transmit wave-guide section associated with the wave-guide.
These and other advantages are provided according to one embodiment of the present invention by an antenna for establishing individual communication links with at least first and second satellites located at different geostationary positions and in close angular proximity to each other. The antenna of this embodiment includes a reflector that directs signals transmitted to and from the first and second satellites. It also includes a first wave-guide positioned with respect to the reflector for establishing a communication link with the first satellite and a second wave-guide positioned with respect to the reflector for establishing a communication link with the second satellite. Importantly, the first and second wave-guides of the antenna are positioned in close proximity with respect to each other so as to establish respective communication links with the closely angular spaced first and second satellites, thereby allowing one antenna to be used to communicate with two closely spaced satellites.
For example, in one embodiment of the present invention, the antenna includes at least one wave-guide that has a dielectric constant greater than that of air. In this embodiment, the dimension of the wave-guide can be controlled or varied in accordance with the dielectric material from which the wave-guide is formed. Specifically, the wave-guide can be decreased in size by using the proper dielectric material such that it may be placed in closer proximity to the other wave-guide. For example, in one embodiment, the wave-guide is formed of a hollow tubular metallic conduit that is filled with a solid dielectric material having a dielectric constant greater than that of air. Since the diameter of the wave-guide for a given frequency is inversely proportional to the square root of the dielectric constant of the material with which the hollow tubular metallic conduit is filled, the diameter of the wave-guide can be decreased by filling the wave-guide with a dielectric material having a higher dielectric constant. By decreasing the diameter of the wave-guide, it can be placed in closer proximity to an adjacent wave- guide so that the wave-guides can establish respective communication links with closely spaced satellites.
In one embodiment, the satellite may be used to form one-way communication links with two closely spaced satellites, where signals from the satellites are received by individual wave-guides. In this embodiment, either one or both of the wave-guides are hollow tubular metallic conduits that are filled with a solid dielectric material having a desired dielectric constant to give the wave-guides proper diameters, such that they be placed in close proximity to one another.
As an example, in one embodiment of the present invention, the first and second satellites are located at geostationary positions that are spaced in a range of 5 degrees or less of arc apart. In this embodiment, in order to establish respective communication links with the satellites, the multibeam antenna includes first and second wave-guides that are positioned within up to 2 inches apart, measured from an axis of the first wave-guide to an axis of the second wave-guide.
In another embodiment, at least one of the first and second wave-guides of the antenna is capable of creating a two-way communication link with its respective satellite, in which the wave-guide both receives signals from and transmits signals to the satellite. As mentioned above, the antenna and multiplexer structure of the present invention can use commercially available wave-guides, which may decrease manufacturing time and cost. As such, in one embodiment, the first wave-guide of the antenna and multiplexer structure of the present invention is a corrugated hollow wave-guide capable of performing two-way communication with the first satellite. The corrugated hollow wave-guide has a width that allows the second wave-guide of the antenna to be positioned in close proximity to the first wave-guide to establish a communication link with the second satellite. In a further embodiment, the corrugated hollow wave-guide is a rectangular corrugated hollow wave-guide having a height of less than three (3) inches and a width of less than an inch and one half (1xc2xd) inches.
In addition to using a corrugated hollow wave-guide for two-way communication with the first satellite, the antenna and multiplexer structure of the present invention may also use a second wave-guide that is dimensioned such that it may be placed in closer proximity to the first feed. For example, in one embodiment, the antenna and multiplexer structure of the present invention includes a second wave-guide for establishing communication with a second satellite, which is a hollow tubular metallic conduit that is filled with a solid dielectric material. The second wave-guide of this embodiment has a dimension that is inversely related to the square root of the dielectric material with which the wave-guide is filled. As such, by using a dielectric material having an increased dielectric constant, the size of the wave-guide can be reduced.
As mentioned above, in addition to antennas, the present invention also provides multiplexer structures for mounting and positioning the wave-guides relative to the reflector of the antenna. Specifically, in one embodiment, the present invention provides a multiplexer structure having first and second feedhorn sections positioned in close proximity to one another. The first feedhorn section is a hollow tubular metallic structure and the second feedhorn section is a hollow tubular metallic conduit that is filled with a solid dielectric material. The multiplexer structure further includes a receive wave-guide section in communication with each respective feedhorn sections and a transmit wave-guide section in communication with the first feedhorn section. The receive wave-guide sections act as conduits for delivering the signals received by the feedhorn sections to respective communication units, such as a TV, computer, etc., associated with the antenna. Further, the transmit wave-guide section acts as a conduit for signals from the transmitter associated with the antenna to the first feedhorn section.
In addition to providing transmit and receive wave-guide sections, the multiplexer structure of the present invention may also provide filters connected to the transmit and receive wave-guide sections. Filters connected to the transmit wave-guide sections prevent signals received by the first feedhorn sections from propagating along the transmit wave-guide section. Further, filters connected to the receive wave-guide sections prevent signals transmitted by the feedhorn sections from propagating along the receive wave-guide sections.
In particular, typically in two-way communication satellite systems, the signals transmitted to the satellites from the transmit feeds are transmitted within a first range of frequencies and signals received from the satellites are received within a second range of frequencies. To prevent received signals from propagating along the transmit wave-guide section, in one embodiment, the multiplexer structure of the present invention includes a filter connected to the transmit wave-guide sections for filtering frequencies in the second range that are received by the feedhorn section. As such, signals received by the feedhorn section do not disrupt the transmitter. Further, and importantly, the multiplexer structure further includes filters connected to the receive wave-guide sections. These filters filter frequencies in the first range, such that signals transmitted from the first feedhorn to the satellite do not propagate along the receive wave-guide sections of the first feedhorn section. Importantly, the filters on the receive wave-guide sections not only prevent signals transmitted by the feedhorn sections from propagating along the receive wave-guide section associated with the feedhorn section, but also prevent propagation of the transmitted signal on the receive wave-guide section of feedhorns that are located adjacent to the transmitting feedhorn section that may receive the transmitted signal due to their proximity to the transmitting feedhorn section.
In some satellite system applications, it is desired to provide maximized communication performance between one of the wave-guides and its associated satellite. For example, some satellite communication systems are used for data transfer, such as Internet communication. In these instances, each bit of data transmitted must be properly received, and as such, increased connection performance is desired. In light of this, in one embodiment, the antenna of the present invention includes a wave-guide positioned such that it is directed at a focal point of the reflector. By positioning the wave-guide such that it is directed at the focal point of the reflector, the signals from the satellite to the wave-guide and signals from the wave-guide to the satellite are better focused, thereby ensuring increased communication performance. In this embodiment, because one wave-guide is positioned with respect to the focal point of the reflector, any second wave-guide is positioned at an offset distance from the first wave-guide for establishing communication with the second satellite.